In the BaZi system (八字, bā zì), interactions happen not only between the earthly branches (地支, dì zhī), but also between the heavenly stems (天干, tiān gān). Five pairs of stems form special combinations — 天干合 (tiān gān hé). In these combinations, one Yin element and one Yang element "attract" each other and theoretically give birth to a new element. The key word is "theoretically": transformation only happens when the right conditions are met.
The formation principle: every 天干合 pairs a Yin and a Yang form of two different elements — stems that sit "next to each other" in the Wu Xing order (五行, wǔ xíng — "five elements"). Numerically: the 1st stem (甲 jiǎ) pairs with the 6th (己 jǐ), the 2nd (乙 yǐ) with the 7th (庚 gēng), the 3rd (丙 bǐng) with the 8th (辛 xīn), and so on. That's exactly why there are precisely six of them.
1 All six 天干合 and what they produce
甲 (jiǎ — the "1st heavenly stem," Yang Wood) and 己 (jǐ — the "6th stem," Yin Earth) form an Earth combination. The classics call it the "union of justice" (中正之合, zhōng zhèng zhī hé); the image is a mighty oak (甲) and fertile soil (己) merging — strength protecting softness. In relationships: attraction between a strong leader and a flexible, supportive partner.
乙 (yǐ — the "2nd stem," Yin Wood, a supple vine) and 庚 (gēng — the "7th stem," Yang Metal, a sword) — the image of a sword cutting down a vine. Metal "wins." The combination creates sharp, precise Metal energy: clarity, discipline, decisiveness. In relationships: softness yields to strength.
丙 (bǐng — the "3rd stem," Yang Fire, the Sun) and 辛 (xīn — the "8th stem," Yin Metal, a jewel). The most unexpected combination: Fire and Metal give birth to Water — the way hot metal, as it cools, condenses moisture. The Water combination carries depth, intuition, mystery. Often tied to an attraction between the "prominent" and the "refined."
丁 (dīng — the "4th stem," Yin Fire, a candle) and 壬 (rén — the "9th stem," Yang Water, the ocean). Water nourishes Wood — a combination of growth. Old texts crown 丁壬合 as the most sensual of the five combinations, calling it a "union of passion" (not the Tao Hua star, 桃花 — that one is read from the branches, not the stems): a candle's flame drawn to the depths of the ocean. The Wood transformation carries growth, expansion, creativity.
戊 (wù — the "5th stem," Yang Earth, a Mountain) and 癸 (guǐ — the "10th stem," Yin Water, mist/dew). A mountain and mist — the image of dawn over a mountain range. Water, warmed by Earth (fire deep within), gives birth to Fire. A combination of transformation: clarity born out of silence. The Fire transformation carries visibility, recognition, publicity.
2 When the transformation is real: the conditions
The classical Ziping school has an important rule: 天干合 doesn't always transform the element. For a real transformation, certain conditions are required:
- 🌿 Support from the season (月令, yuè lìng — the "month's command"): if the month branch supports the new element, the transformation is confirmed;
- 🔢 The presence of the new element elsewhere in the chart: if there's no sign of Earth anywhere, the 甲己 combination only produces "tied-up-ness," not actual Earth;
- 🚫 No blocking: if another stem sits between 甲 and 己, the combination is broken.
3 A combination as "tied up": the most important practical consequence
Once a 天干合 actually holds — the two stems sit next to each other with nothing breaking the link — it has one near-certain consequence: both stems become "tied up," merged with each other, and temporarily lose their independent function.
What does this mean in practice? If your 用神 (yòng shén — the "Useful God," your chart's key resource) enters a combination with another stem, its energy is "diverted" from doing its job. If the element itself doesn't change, that tied-up state alone is called 合而不化 (hé ér bù huà — "combined but not transformed"), also known as 合絆 (hé bàn, "bound by the combination"). If the element does change, it's 合而化 (hé ér huà — "combined and transformed"). Either way, it can be either a blessing or a problem.
4 天干合 and romance: attraction through the chart
In compatibility reading practice, a 天干合 between the stems of two people — especially between their Day Masters (日主, rì zhǔ) — points to a chemical attraction. It isn't a guarantee of happiness, but it is a signal: the two people are "drawn" to each other at the level of elemental nature.
Considered especially romantic:
- 💫 丁壬合 (dīng rén hé): the most "romantic" of the combinations — old texts call it a "union of passion" (distinct from the Tao Hua star, 桃花);
- ✨ 丙辛合 (bǐng xīn hé): an attraction between the public and the refined, brightness and depth;
- 真 甲己合 (jiǎ jǐ hé): the "union of justice" (中正之合) — strength protecting softness, the classic "protector and protected" pair.
5 天干合 vs 地支合 (dì zhī hé): the difference in scale
The heavenly stems (天干) govern outward expression, visible life, the social sphere. The earthly branches (地支) govern inner life, destiny, deep processes. So:
- 天干合 — influences professional relationships, public life, career alliances;
- 地支合 (六合, liù hé) — influences deep relationships, destiny, long-term partnerships.
Is there a Heavenly Combination in your chart?
The Full reading lists the structural connections in your natal chart, 天干合 included, and the years your calculated cycles bring them out.
Personal Reading “Standard” · $19.90 Order the Full Reading · $49.90 Calculate my chart for free →